This invention is directed to a method of making elastic composite materials including elastomeric adhesive film reinforced with elastic strands which significantly improves tension decay and adhesion properties of the material.
Personal care garments often include elasticized portions to create a gasket-like fit around certain openings, such as waist openings and leg openings. Laminates made from conventional elastic strands and elastic attachment adhesive are often used to create such elasticized portions. However, such laminates can be rough and uncomfortable. Furthermore, such laminates may cause red-marking on a wearer's skin if the fit is too tight and may result in leakage from the garment if the fit is too loose.
Elastomeric adhesive compositions are multifunctional in the sense that they function as an elastomer in a nonwoven composite while also serving as a hot melt adhesive for bonding substrates. Elastomeric adhesive compositions in the form of elastomeric adhesive films are currently recognized as suitable for use in the manufacture of personal care articles. More particularly, elastomeric adhesive compositions can be used to bond facing materials, such as spunbond, to one another while simultaneously elasticizing the resulting laminate. The resulting laminate can be used to form an elastomeric portion of an absorbent article, such as a region surrounding a waist opening and/or a leg opening.
Non-woven elastic adhesive film laminates may require high output of adhesive add-on to achieve a tension target for product application. High add-on of the film laminate may generate a bulky, thick feel and appearance, and high cost. Furthermore, the high adhesive output requirement for the film formation would make on-line processing even more difficult due to the limitation of hot melt equipment output capacity. Also, such film lamination processes are relatively complex and need more precise control than strand lamination since a film edge thinning effect may cause the film to break during stretching.
Some elastomeric adhesive compositions lose their adhesiveness when the compositions are stretched and then bonded between two nonwoven substrates. The elasticity of these elastomeric adhesive compositions (in terms of tension decay) is negatively affected when laminates including the compositions are aged at elevated temperatures.
One type of elastomeric adhesive composition having improved elastic and adhesion properties that also provides adequate tension for product application is made up of a combination of extruded reinforcing strands and elastomeric adhesive film. A layer of spunbond or other facing material can be laminated along both surfaces of the film to provide elastic composite laminates. The combination of reinforcing strands and the elastomeric adhesive film significantly and advantageously reduces the rate and extent of tension decay, as well as improving adhesion properties of the spunbond laminates compared to spunbond laminates including elastomeric adhesive film without reinforcing strands.
It is known to make such strand-reinforced composites and laminates by extruding the elastomeric adhesive film and the reinforcing strands separately, followed by independent stretching prior to lamination between nonwoven facing materials. However, there are several shortcomings associated with independent stretching of strands and film elements. These shortcomings include a need for more equipment to control/stabilize the process, plus the strands need to be aligned to have uniform spacing. Additionally, frequencies of film or strand break are high especially in high stretch ratio and high web speed. Such drawbacks make the laminate production process difficult and complex.
With the foregoing in mind, it is a feature and advantage of the invention to provide a method of making strand-reinforced elastic composites and laminates with improved processability in which film breakage, strand breakage, and strand alignment problems are minimized or avoided.